1. Field of the Invention
The present invention relates generally to a laser measurement tool that measures vibrations at locations of interest in response to an ultrasonic operator and, more particularly, provides useful information with large sample rates in highly dynamic vibration noisy environments and/or relatively solid structures.
2. Description of the Prior Art
According to a report released in 2005 by the American Society of Civil Engineers (ASCE), a total of about 160,570 bridges, or just over one-quarter of the nation's approximately 590,750-bridge inventory, were rated structurally deficient or functionally obsolete. The basic cause of failure is metal fatigue brought on by many possible intermediate causes. Every State has a large number of bridges. For example, Rhode Island has about 753 bridges, California has about 24,028 bridges, and Texas has about 49,504 bridges. Bridges, like any fabricated structure, can fail for many reasons. Prevention of such failures is of paramount importance.
Many patents attempt to detect structural failures by a general method called Structural Health Monitoring (SHM), a methodology that involves the placement of sensors inside a structure, which can communicate structural status to inspectors. However, the location of the sensor(s) is problematic. For example, a crack could form almost any place in a gusset plate. Moreover, when a fatigue crack becomes visible, only a small percentage of the life remains, perhaps as little as about 10%. The likely list of causes for bridge disasters include the following: fatigue cracks, corroded gusset plates, frozen bearings, overweight construction materials, weather, de-icing materials, and an unstable bridge deck.
It is highly desirable that new technologies be available to local, state and federal agencies for quickly scanning a large number of bridges to locate any failure points to avoid potentially devastating disasters.
The following U.S. Patents describe various prior art systems that may be related to the above and/or other problems:
U.S. Pat. No. 7,286,964, issued Oct. 23, 2007, to Kim, discloses methods and recordable media for monitoring structural health conditions. A method is disclosed for interrogating for damage of a host structure using a diagnostic network patch (DNP) system having patches. An interrogation module partitions the plurality of patches in subgroups and measures the sensor signals generated and received by actuator and sensor patches, respectively. Then, a process module loads sensor signal data to identify wave modes, determine the time of arrival of the modes and generate a tomographic image. It also determines distribution of other structural condition indices to generate tomographic images of the host structure. A set of tomographic images can be stacked to generate a hyperspectral tomography cube. A classification module generates a codebook based on K-mean/Learning Vector Quantization algorithm and uses a neural-fuzzy-inference system to determine the type of damages of the host structure.
U.S. Pat. No. 7,281,428, issued Oct. 16, 2007, to Kim, discloses interrogation systems for monitoring structural health conditions. An interrogation system includes at least one wave generator for generating a wave signal and optical fiber sensors applied to a structure. The interrogation system also includes at least one electronic module for generating an input sensor signal and sending the input sensor signal to the optical fiber sensors. Each optical fiber sensor impresses the wave signal onto the input sensor signal to generate an output sensor signal that is frequency shifted from the input sensor signal. The electronic module generates an information signal in response to the output sensor signal. The interrogation system also includes a signal processing unit and a relay switch array module that has relay switches. Each relay switch relays the information signal to the signal processing unit and the signal processing unit generates a digital sensor signal that is subsequently sent to a computer.
U.S. Pat. No. 7,277,573, issued Oct. 2, 2007, to O'Brien, Jr., which is incorporated herein by reference, discloses a multi-stage method for automatically characterizing data sets containing data points which are each defined by measurements of three variables as either random or non-random. A three-dimensional Cartesian volume which is sized to contain all of a total number N of data points in the data set which is to be characterized. The Cartesian volume is partitioned into equal sized cubes, wherein each cube may or may not contain a data point. A predetermined route is defined that goes through every cube one time and scores each cube as a one or a zero thereby producing a stream of ones and zeros. The number of runs is counted and utilized to provide a Runs Test, which predicts if the N data points in any data set are random or nonrandom. Additional tests are used in conjunction with the Runs Test to increase the accuracy of characterization of each data set as random or nonrandom.
U.S. Pat. No. 7,267,008, issued Sep. 11, 2007, to Gordon et al, discloses a transducer for use in a structural health monitoring system that includes a single transducer element. The transducer includes a transmit assembly coupled to the single transducer element. This assembly is configured to produce a multi-cycle square wave drive signal for stimulating the transducer. Additionally, a transmit/receive switch coupled to the single transducer element is provided. This assembly is configured to isolate the drive signal from the receive assembly used to sense the electrical signal generated from any received elastic waves.
U.S. Pat. No. 7,246,521, issued Jul. 24, 2007, U.S. Pat. No. 7,197,931, issued Apr. 3, 2007, and U.S. Pat. No. 7,117,742, issued Oct. 10, 2006, to Kim, disclose sensors and systems for monitoring structural health conditions. A device is provided for monitoring structural health conditions including a dielectric substrate, a piezoelectric device for actuating and/or sensing waves, a molding layer deposited over the piezoelectric device, a cover layer deposited over the molding layer and a hoop layer surrounding the piezoelectric device and being attached to the substrate. The device further includes an optical fiber coil sensor attached to the dielectric substrate, where the coil sensor has a rolled optical fiber cable and a coating layer applied to the rolled optical fiber cable. A diagnostic patch network includes a plurality of patch sensors attached to a host structure and a bridge box connected to the patch sensors. The bridge box sends information of structural health conditions to and receives power from a ground control system using a wireless communication technique.
U.S. Pat. No. 7,080,555, issued Jul. 25, 2006, to Austin et al, discloses a distributed real time health monitoring system for monitoring of acoustic emission signals from different regions of a structure such as aircraft or spacecraft structures. The health monitoring system has its analysis and prognosis intelligence distributed out to the local regions being monitored and therefore does not require extensive cabling systems to carry the high bandwidth information characteristic of acoustic emission.
U.S. Pat. No. 7,075,424, issued Jul. 11, 2006, to Sundaresan et al, discloses a sensor array for non-destructively monitoring a structure to detect a critical structural event. The sensor array includes a plurality of discrete sensor nodes, each of the discrete sensor nodes producing an electrical signal in response to a structural event. A signal adder is electrically connected to the plurality of discrete sensor nodes for receiving and combining the electrical signal from each of the discrete sensor nodes to form a single sensor array output signal. A signal processing module then receives and processes the single sensor output signal. In the preferred embodiment, the signal processing module uses the time interval between the electrical signals from each of the discrete sensor nodes formed into a single sensor array output signal to calculate the location of the critical structural event. Also, in the preferred embodiment, a data collection system is located downstream of the sensor processing module.
U.S. Pat. No. 6,826,982, issued Dec. 7, 2004, to O'Brien et al, which is incorporated herein by reference, discloses a method and apparatus for detecting and monitoring fractures in a structure by monitoring acoustic energy transmitted within the structure by receiving continuously over a period of time electrical signals from a plurality of acoustic transducers carried by the structure in a pulse processor to form data bursts from pulses in the signals and deriving, for each of a plurality of the data bursts, delta-t values representing the differences between burst arrival times at each sensor, the delta-t values forming a delta-t pattern, and generating a damage indication signal when the delta-t pattern is repeated to a predetermined degree.
U.S. Pat. No. 6,399,939, issued Jun. 4, 2002, to Sundaresan et al, discloses a sensor array for nondestructively monitoring a structure to detect a critical event. The sensor array includes a plurality of discrete sensor nodes, each of the discrete sensor nodes producing an electrical signal in response to a structural event. In the preferred embodiment, the sensor nodes include a plurality of piezoceramic fibers arranged in a planar array in which the fibers are aligned substantially parallel to each other, each of the fibers having a plurality of polarized regions that are substantially oriented according to their polarity in either a series, parallel, or combined arrangement of series and parallel orientations, and an electrical interface connecting the plurality of polarized regions of each fiber in series with one another. A signal adder receives and combines the electrical signals from each of the discrete sensor nodes to form a single sensor array output signal. In the preferred embodiment, the electrical interface further includes at least one electrical bus substantially aligned with the fibers and a signal processing module for receiving and processing the single sensor output signal. The signal processing module is linked through the digital data bus to a central processing unit. The plurality of discrete sensor nodes may further be divided into discrete subgroups, each located at a different structural location to provide a degree of sensing and determining the location of the structural event. In the preferred embodiment, the discrete sensor nodes are electrically connected in series, thereby forming a continuous series connection between each of the discrete sensor nodes to improve the likelihood that a critical structural event will be detected.
U.S. Pat. No. 5,505,090, issued Apr. 9, 1996, to Webster, discloses an apparatus for non-destructively inspecting for faults in or beneath the surface of structures, such as debonds or delaminations in composite materials, or cracks, broken stringers, delaminations and the like in semi-monocoque structures, which includes at least one spark gap discharge device displaced from the test object which focuses an acoustic pulse onto a small local area of the object for vibrationally exciting the surface of that area. A laser Doppler camera system, also displaced from the test object directs a laser beam onto the excited area and derives from light energy reflected back from the excited area the velocity of out-of-surface displacement of, and relaxation frequencies generated by, the surface of the excited area and provides an indication of whether a fault is present in that area. Acoustic pulses and the laser beam are directed to successive local areas in synchronism according to a scanning pattern, at each of which the reflected light energy is analyzed, following which the acquired data is processed and visually displayed in a manner which clearly indicates the presence of a fault and its location and enables the operator to further analyze the data to ascertain the type and extent of the fault.
The article “Model for continuously scanning ultrasound vibrometer sensing displacements of randomly rough vibrating surfaces,” by Ratilal et al., from the Journal of Acoustical Society of America, February 2007, 0001-4966/2007/121(2)/863/16, discloses an analytic model for the time-dependent ultrasound field reflected of a randomly rough vibrating surface for a continuously scanning ultrasound vibrometer system in bistatic configuration. The model incorporates the beam patterns of both the transmitting and the receiving ultrasound transducers and the statistical properties of the rough surface. Motions of the vibrometer over the randomly rough surface leads to time dependent scattering noise that causes a randomization of the received signal spectrum. Simulations with the model indicate that the surface displacement and velocity estimation are highly dependent upon the scan velocity and projected wavelength of the ultrasound vibrometer relative to the roughness height standard deviation and correlation length scales of the rough surface. The model is applied to determine limiting scan speeds for ultrasound vibrometer measuring ground displacements arising from acoustic or seismic excitation to be used in acoustic landmine confirmation sensing.
The above cited prior art does not disclose a laser vibration analyzer which provides useful large sample size measurements involved in scanning structures carried out in the dynamic environment of nature, which includes the presence of vibrations, background noise, traffic noise, transformer noise, engine (machinery) noise, seismic noise, and other interferences inherent when making measurements in the real world including during operation. The solutions to the above described and/or related problems have been long sought without success. Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.